The most prolific form of messaging employed in mobile communication systems is the Short Message Service (SMS). Typically Messages are sent from the originating device to a Short Message Service Centre (SMSC) which provides a store-and-forward mechanism. Transmission of short messages between the SMSC and the handset is done using the Mobile Application Part (MAP) of the SS7 protocol. Messages are sent with the MAP mo- and mt-ForwardSM operations, whose payload length is limited by the constraints of the signalling protocol to precisely 140 octets (140 octets=140*8 bits=1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet (shown below), the 8-bit data alphabet, and the 16-bit UTF-16/UCS-2 alphabet.
Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual Short Message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters (including spaces). Support of the GSM 7-bit alphabet is mandatory for GSM handsets and network elements, [15] but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian) must be encoded using the 16-bit UCS-2 character encoding (Unicode). Routing data and other metadata is additional to the payload size.
If a recipient is not reachable, the SMSC queues the message for later retry. Some SMSCs also provide a “forward and forget” option where transmission is tried only once. Accordingly message delivery is best effort, so there are no guarantees that a message will actually be delivered to its recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks.
In recent years additional message services such as instant message and email have migrated to the mobile environment. In the standard desktop environment Instant Messaging (IM) provided real-time text-based or near real-time communication between two or more participants over a network. Thus the key distinction between IM from such services as email is the perceived synchronicity of the communication between users, messaging is done in real or near real-time. Instant messages are typically logged in a local message history which closes the gap to the persistent nature of emails and facilitates quick exchange of information like URLs or document snippets (which can be unwieldy when communicated via telephone). IM allows effective and efficient communication, featuring immediate receipt of acknowledgment or reply.
Mobile Instant Messaging (MIM) differs slightly to that of standard desktop IM application. MIM is a presence enabled messaging service which attempts to transpose the desktop messaging experience to the usage scenario of being on the move. While several of the core ideas of the desktop experience on one hand apply to a connected mobile device, others do not. For example some of the form factor and mobility related differences need to be taken into account in order to create a really adequate, powerful and yet convenient mobile experience such as bandwidth, memory size, availability of media formats, keypad based input, screen output, CPU performance and battery power are core issues that desktop device users and even nomadic users with connected network.
As mentioned above as mobile data networks can be unreliable and messages may go missing (message delivery being best effort). Existing mobile Instant Messaging (IM) “gateway” products treat IM messages as “casual chat”. As such there is no guarantee that the message will be delivered to the intended recipient as MIM do not see the loss of a message as being of consequence. As such the current implementations of MIM are not readily suited to a business environment or other applications where the delivery of information is critical.
As discussed above most existing messaging systems (e.g. SMS) offer limited storage capacity. In the case of SMS a local PC backup/archive may be required to provide any sort of message backup capability and then the process is manual in nature. A user wishing to save messages must perform this manual process prior to deleting messages on their mobile device to free up space for new messages.
Accordingly there is a need to provide a reliable messaging solution that will be accepted by a casual as well as a business or critical user. It would also be advantageous to provide a facility to enable users to backup messages sent and received for later review.